Different machine screens, such as disc filters and drum filters, are used for removing liquid from a mixture consisting of liquid and dry solids. A disc filter typically comprises a plurality of triangular filter segments arranged in a rotating frame onto which segments are arranged filter bags made of filter cloth. The liquid in the mixture to be filtered is allowed to penetrate through the filter cloth and further into a segment through openings extending to the surface of the filter segment. In addition to the segments, depending on the structure of the filter, different box-like and cylinder-like pieces and other elements are used onto which a bag or a similar filtering module made of filter cloth is stretched by means of different mechanical tightening parts or, nowadays increasingly often, by thermal contraction. It has been found out that if compact filter cloth is in use allowed to be pressed tightly against the surface of the filtering element, the flow of the passed liquid is hindered between the filtering cloth and the element to the openings of the element. In order to prevent this problem, a separate “additional wire bag” has been introduced between the actual filtering bag and the filtering element. The backing wire bag is made of a netlike texture forming a loose, highly permeable layer in the transverse direction of the surface of the cloth between the compact filtering bag and the surface of the element. Although such a separate backing wire bag does work relatively well in practice, fitting the backing wire bag is, however, an additional stage of operation. Furthermore, the manufacturing also causes additional costs.
SE 431 826 discloses filter cloth for separating solid particles and liquid, comprising at least two interwoven layers: a filtering layer and a supporting layer. In the supporting layer, i.e. in the portion facing the filtering element, thicker yarns are to be used in order to achieve a more coarse bottom. A drawback of the disclosed solution is, however, that the liquid that has already passed the filtering layer in the direction of the surface of the filtering element flows inside the supporting texture of the filter cloth. As normally, the texture comprises yarns travelling crosswise and having different directions, whereby the yarns form obstacles to an efficient flow of liquid.